Hydrocarbon conversion process with subsequent reforming of selected hydrocarbon fractions



2,915,453 QUENT Dec. 1, 1959 v. HAENsEL ETAI- HYDROCARBON CONVERSIONPROCESS WITH SUBSE REFORMING OF SELECTED HYDROCARBON FRACTIONS Filed may26, 1955 United States Patent Office 2,915,453 Patented Dec. 1, 1959HYDRCRBON CONVERSION v PROCESS WITH SUBSEQUENT REFORMNG OF SELECTEDHYDROCARBON FRACTIONS Application May '26, 1.955, serial No. 511,288 lsclaims. (ci. 20s-64) This invention relates to the catalytic conversionof hydrocarbons boiling within the gasoline range. It is morespecifically concerned with a novel combination of sol-vent extraction,fractionation, and catalytic reforming.

The refining industry has been deeply concerned with recent trends inbothth'e automotive and refining fields which give rise top'r'edictionsof unprecedented increases in gaso-line quality in the near future. Inrecognition of these trends, research efforts have been directed towardthe development ofa practical method for the production of such superqu'al'ityg`asolines.

One process that has recently received commercial attention is thecatalyticreformin'g process. The term reforming is lwell known in' thepetroleum industry and refers to the treatment of gasoline fractions toimprove the antiknock characteristics thereof. A highly successful andeconomical reforming process that has achieved Wide 'commercialacceptance is described in U.S. Patent No. 2,479,110, issued toVladimirjHaensel. However, the present reforming' processes are alllimited by decreasing yields at increasing octane numbers. There arealso other limitations. For example, when a full boiling rangestraight-run gasoline or a relat-ively wide boiling range nap-htha isreformed in the presence of a catalyst that promotes dehydrogenation ofnaphthenes and hydrocracking of parafiins, relatively poor yields andconsiderable fouling of lthe catalyst are obtained when the operatingconditions are selected to obtain large octane number appreciation. Thisapparently is due to the fact that the relatively severe operatingconditions that must be maintained in order to satisfactorily upgradethe higher boiling paraflinic constituents of the feed are too severefor some of the other constituents. The result is that an appreciablepart of the feed stock is undesirably converted to gases and to catalystcarbon. Therefore, under the usual conditions of operation the yield ofliquid product andl catalyst life are limited to a considerable extentby and primarily dependent on the decomposition and carbon formingtendencies of the higher boiling paraftinic co-nstituents and thearomatic constituents. The higher boiling paraffinic constituents maydecompose to form coke on the catalyst and the aromatic 4constituentsalso deposit coke or carbonaceous material on `the catalyst by reactingwith each other and forming polynuclear aromatics which are thecarbonaceous materials that foul the catalyst. We have invented a methodof reforming which largely overcomes these objectionable features of theprior art reforming processes.

It is an object of the present invention to treat a full boiling rangestraight-run gasoline or a fraction thereof in such a manner thatincreased yields of high octane number gasoline and aromatics and longercatalyst life are obtained.

In one embodiment the present invention relates to a process foreffecting an improved yield of high octane number gasoline whichcomprises subjecting hydrogen and a gasoline fraction to reforming in afirst reforming z one, effecting the separation of at least a portion ofthe resultant reformed stream into a predominantly parafnic fraction anda predominantly aromatic fraction, fractionating at least a portion ofsaid predominantly parafilnic fraction into a low boiling fraction and ahigh boiling fraction and subjecting at least a portion of said lowboiling fraction to reforming in a second reforming zone.

In another embodiment the present invention relates tol a process foreffecting an improved yield of high octane number gasoline whichcomprises subjecting hydrogen and a gasoline fraction to reforming in afirst reforming Zone in the presence of a catalyst that promotesdehydrogenat-ion of the naphthenes and hydrocracking of parafins,subsequently cooling the resultant reformed stream and effecting theseparation thereof to provide a gaseous hydrogen-containing the streamand an aromaticrich hydrocarbon stream, passing the latter to afractionating zone` and removing normally gaseous components therefrom,treating the remaining fraction in a separation zone, withdrawing fromsaid separation Zone a predominantly parafiinic fraction and separatelywithdrawing a predominantly aromatic fraction, subjecting at least aportion of said predominantly parafiinic fraction to fractionation in afractionation zone, separately withdrawing from said fractionation zonea low boiling fraction and a high boiling fraction, subjecting at leasta portion of said low boiling fraction to reforming in a secondreforming zone in the presence of a catalyst that promotesdehydrocyclization of parafiins, and recycling at least a portion ofsaid high boiling fraction to said first reforming zone.

In a specific embodiment the present invention relates to a processwhich comprises subjecting a gasoline fraction to reforming in afirst'reforming zone, at a temperatureof from about 600 F. to about1000"l F., a pressure of from about 200 to about 1000 p.s.i., withhydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5 toaboutV 20 mols of hydrogen per mol of hydrocarbon, in the presence of acatalyst comprising alumina, from about 0.01% to about 1% by weight ofplatinum and from about 0.1% to about 3% by weight of combined halogen,Subsequently cooling the resultant reformed stream and effecting theseparation thereof` to pro-vide a gaseous hydrogen-containing stream andaromatic-rich hydrocarbon stream, introducing said aromatic-richhydrocarbon stream to a first fractionation zone to remove normallygaseous components therefrom, passing an aromatic-rich hydrocarbonstream from said first fractionation zone to an extraction zone whereinsaid stream is countercurrently contacted with a selective solventcontaining diethylene glycol and from about 1% to about 20% by weight ofwater, separately removing from said extraction zone an extractcontaining said solvent and a substantial amount of aromatics and araffinate containing a substantial amount of parahinic hydrocarbon,introducing said extract to a stripper, removing overhead from saidstripper an aromatic-containing stream, removing as bottoms from saidstripper'a solvent stream and recycling said solvent stream to saidextraction zone, subjecting said raffinate to fractionation in a secondfractionation zone, separately withdrawing from said secondfractionation zone a low boiling fraction and a high boiling fraction,subjecting at least a portion of said low boiling fraction to contact ina second reforming Zone with a reforming catalyst at a pressure lowerthan in said first reforming zone, and recycling at least a portion ofsaid high ,boiling fraction to said first reforming zone.

Briefly, the present invention provides a method for effecting animproved yield of high octane gasoline from a hydrocarbon stream boilingin the gasoline range which comprises 'subjecting the hydrocarbon streamto reforming in the presence of hydrogen and a suitable reformingcatalyst. In the rst reforming zone naphthenes are dehydrogenated toaromatics and heavy parains are hydrocracked to lower boiling parains.It is also preferred that the conditions and the catalyst in the firstreaction zone be such that there is some paraflin isomerization and someparaffin dehydrocyclization. The resulting reformed stream is cooled andthe separation thereof effected to provide a gaseous hydrogen-containingstream and an aromatic-rich hydrocarbon stream. The aromatic-richhydrocarbon stream is fractionated to reject the normallyv gaseoushydrocarbons produced in the process and the resultant liquid is passedto a separation zone in which the recovery of aromatic hydrocarbons iseffected. The resulting non-aromatic or paraflnic hydrocarbon stream ispassed to a fractionation zone wherein the raffinate or parafnichydrocarbon stream is fractionated into at least a low boiling fractionand a high boiling fraction. The low boiling fraction is passed to asecond reforming zone wherein it is contacted with a dehydrocyclizationcatalyst while in the presence of hydrogen. The second reforming zone isat a pressure at least 75 pounds per square inch lower than the pressurein the lirst reforming zone and preferably at least 100 pounds persquare inch lower than they pressure in the first reforming zone. ln thesecond reaction zone the temperature is preferably higher than thetemperature in the first reforming zone. 1n the second reforming zonethe low boiling parafns are dehydrocyclicized to form additionalaromatic hydrocarbons. The product from the second reaction zone ispassed to the tirst fractionation zone and from there the stream followsthe same route as the effluent from the first reforming zone. The highboiling fraction removed from the second fractionation zone may befurther fractionated and in a preferred embodiment of the presentinvention at least a portion of the high boiling fraction is recycled tothe first reforming zone.

A feature of our process is that mild hydrocracking conditions may beemployed in the first reforming step. Generally more severe conditionsare necessary to dehydrocyclicize lower boiling straight chain parains-to form aromatics than to dehydrogenate a cycloparafin or naphthene toform an aromatic. Reforming of the low octane number lower boilingparaftins in a separate reaction zone results in their beingdehydrocyclicized to aromatics and/ or their being converted to lowerboiling high octane number parains without the excessive production ofgaseous hydrocarbons that would result were these lower boiling parafhnssubstantially completely reacted in the tirst reforming reactorcontinued at conditions of high severity. Therefore, a feature of ourprocess is that the conditions in the second reforming zone may besevere enough to convert a substantial portion of the parain toaromatics while at the same time minimizing undesirable side reactionswhich otherwise reduce yields of useful gasoline products. Ashereinbefore mentioned, one of the chief reasons for deposit of carbonor carbonaceous material on the catalyst is the reaction of aromatics toform polynuclear aromatics. In our process, however, the aromatics areremoved and, therefore, substantially less carbon is formed on thecatalyst with resultant longer catalyst life. High severity operation inthe presence of aromatics is also not desirable from considerations ofchemical equilibria involved, as in such operations the it undergoesdehydrocyclization at reasonable operating conditions, a feature of ourprocess is that isohexanes may be continuously removed and the normalhexane introduced to the second reaction zone thus obtainingsubstantially complete conversion of low octane normal hexane to muchhigher quality isohexanes with almost no restrictions in yield due tochemical equilibrium con siderations. I

Accordingly, the aromatics are separated from the parattns and thenaphthenes in the reformate from the first reaction zone for severalreasons. One reason 1s that if the aromatics were introduced to thesecond reaction zone it would result in lower overall yields ofreformate presumably due to the conversion of the aromatics to gaseoushydrocarbons and to hydrocarbons boiling above the gasoline range.Another reason is that higher concentrations of aromatics in thereaction zone tend to result in a greater carbon deposition andconsequently a shorter catalyst life. Still another reason, which hashereinbefore been mentioned, is that high concentra tions of aromaticsin the reaction zone tend to suppress the dehydrogenation of naphthenesto aromatics and to suppress the dehydrocyclization of paraflins toaromatics, said dehydrogenation and said dehydrocyclization beingequilibrium reactions.

The charge stocks which may be reformed in accordance with my processcomprise hydrocarbon fractions that boil within the gasoline range andthat contain naphthenes and parains. The preferred stocks are thosecous'isting essentially of naphthenes and parains, although aromaticsand minor amounts of olefns may be present. This preferred classincludes straight-run gasoline, natural gasoline and the like. Thegasoline fraction may be a full boiling range gasoline having an initialboiling point within the range of from about 50 F. to about 100 F. andan end boiling point within the range of from about 350` F. to about 425F. or it may be a selected fraction thereof which usually is a higherboiling fraction commonly referred to as naphtha and having an initialboil-- ing point within the range of from about 150 F. to about- 250 F.and an end boiling point within the range of from about 350 F. to about425 F. Mixtures of the various gasolines and/or gasoline fractions mayalso be.

aromatics in the feed limit the extent to which such aro matics can beformed from naphthenes and parans. In contrast, however, the use of ourprocess involves the removal of a substantial portion of the aromaticsfrom the charge to the second reaction zone which thus permits theformation of additional aromatics unrestricted by the limitations ofchemical equilibria.

Similarly, the isomerization of low octane rating straight chainparallins to higher octane quality branched chain structure parains isan equilibrium reaction. As the isomerization of normal hexane isimportant to achieve in up-grading gasolines, due to the very limitedextent that used and thermally cracked and/or catalytically crackedgasolines may be used as charging stock. However, whenthese unsaturatedgasoline fractions are used, it is preferred that they be used either invadmixture with a straight-run or natural gasoline fraction, or elsehydrogenated prior to use.

In a preferred operation in the rst reforming step, wherein the chargeis subjected to hydrocracking and aromatization, the contact is made ata pressure of from about 200 to about 1000 pounds per square inch. Inthe subsequent catalytic contacting step in the second reform ing zone,the C6+ low boiling hydrocarbon fraction contacts the catalyst at alower pressure, said pressure being at least 75 pounds per square inchand preferably at least pounds per square inch lower than the pressurein the first reforming step. It is also to be noted that certain of thetive-membered naphthenes such as methylcyclopentane which are present inthe low boiling fraction of the raflinate, are not completely convertedto benzene in the 'rst reforming step so that a subsequent contact afterremoval of aromatics permits further dehydrogenation and conversion ofsuch fractions to benzene and other aromatics while the normal hexane issubjected to dehydrooyclization to produce aromatics of higher octanenumber and/or isomerization to branched chain paratlins of higher octanenumber. y

A preferred operation effects the recycle of the hydrogen stream beingseparated from the reformed gasoline stream into contact with the chargestream in order to provide added hydrogen to the catalytic reformingzone. Similarly, hydrogen separated from the second reforming zone maybe recycled to the latter to provide the presence of additional hydrogenduringthe catalytic contact of the parains.

Various types of desirable and suitable catalysts may be utilized withineach stage of the process; however, the preferred operation utilizesplatinum containing catalyst in each of the contact zones. The catalyststhat may be used in the first reforming zone of our invention comprisethose reforming catalysts thatv permit dehydrogenation of naphthenichydrocarbons, hydrocracking of paraffinic hydrocarbons and isomerizationof parai'nic hydrocarbons. A satisfactory catalyst comprises aplatinumalumina-silicacatalyst of the type described in U.S. Patent No.2,478,916, issued August 16, 1949. A preferred catalyst comprises aplatinum-alumina-combined halogen catalyst of the type described in U.S.Patent No. 2,479,109, issued August 16, 1949. Other'catalysts such asmolybdena-alumina, chromia-alumina, and platinum on a carrier or supportsuch as a cracking catalyst base may be used. In the second reformingzone as well as in the first reforming zone, the platinum concentrationin the catalyst may range up to about by weight or more of the alumina,but a desirable catalyst may be provided to contain as low as fromlabout 0.01% to about 1% by weight of platinum. The halogen ions may bepresent in an amount of from about 0.1% to about 8% by weight of thecatalyst but preferably are present in an amount of from about 0.1% toabout 3% by weight of the alumina on a dry basis. Also, while any of thehalogen ions provide a desirable catalyst, the fluoride ions areparticularly preferred and next in order are the chloride ions, thebromide ions and iodide ions. In the second stage of catalyst contactwhere the non-aromatic C6+ fraction undergoes dehydrocyclization theremay be a lesser quantity of platinum present in the catalyst.

Except for pressure level, the operating conditions maintained in eachof the two reforming stages of our process are essentially the same. Theconditions in the first zone should be such that substantial conversionof naphthenes to aromatics and relatively mild hydrocracking of parafinsare induced; and, further, the operating conditions in the second zoneshould be such that there is a substantial conversion of parafiiniccompounds to aromatics by dehydrocyclization as well as isomerization ofparans such as the isomcrization of normal hexane to isohexane. Whenemploying platinum-alumina-combined halogen catalyst in both of thereforming zones, the conditions in each are usually a temperature withinthe range of from about 600 F. to about 1000 F., and a weight hourlyspace velocity of from about 0.5 to about 20. The weight hourly spacevelocity is defined as the weight of oil per hour per weight of catalystin the reaction zone. It is preferred that the reforming reaction inboth of the reaction zones be conducted in the presence of hydrogen. Inone embodiment of the process, sufficient hydrogen will be produced inthe reaction to furnish the hydrogen required in the process and,therefore, it may be unnecessary to introduce hydrogen from an externalsource or to recycle hydrogen within the process. However, it will bepreferred to introduce hydrogen from an external source generally at thebeginning of the operation and to recycle hydrogen within the process inorder to be assured of a sufficient hydrogen atmosphere in each of thereaction zones. The hydrogen present in each of the reaction zones willbe within the range of from about 0.5 to about 20 mols of hydrogen permol of hydrocarbon. In some cases, the gas to be recycled will containhydrogen sulfide introduced with the charge or liberated by the catalystand it is within the scope of the present invention to treat thehydrogen-containing gas to remove hydrogen sulde or other impurities'before recycling the hydrogen to the reforming zone. The pressure in thefirst reaction zone is from about 200 to about 1000 pounds per squareinch. The pressure in the second reaction zone is lower, and is at least.75 pounds per square inch lower and prefcrably at least about 100pounds per square inch lower.

' of product.

The pressure range, therefore, is from about to about 925 p.s.i. Thetemperature in the second reaction zone is preferably higher than in thefirst reaction zone. The conditions are such that there aresubstantially no olefins present in the product streams from the firstand the second reaction zones.

The effluent from the first reforming zone along with the effluent fromthe second reforming zone is usuallyv passed to a stabilizer whicheffects the separation of normally gaseous material which compriseshydrogen, hydrogen sulfide, ammonia and hydrocarbons containing one tofour carbon atoms per molecule from the normally liquid hydrocarbons. Ina preferred embodiment of the invention the efliuent from the firstreaction zone and the effluent from the second reaction zone areintroduced to a common stabilizer since the use of one stabilizer foreach of the effluents is of decided economic advantage. The stabilizedliquid is then passed to a separation zone to produce a moreconcentrated aromatic fraction. The separation of a more concentratedaromatic fraction may be accomplished inl any conventional manner suchas solvent extraction, solid absorption, fractional crystallization, theuse of urea adducts, molecular sieves, etc. however, the solventextraction process is particularly preferred in the present inventionsince its use generally produces best results.

Solvent extraction processes are used to separate certain components ina mixture from other components thereof by a separation process basedupon a difference in solubility of the components in a particularsolvent. It is frequently desirable to separate various substances bysolvent extraction: when the substances to be separated have similarboiling points, are unstable vat temperatures at which fractionation iseffected, form constant boiling mixtures, etc. It is particularlydesirable to separate aromatic hydrocarbons from a petroleum fractioncontaining these aromatic hydrocarbons by solvent extraction because apetroleum fraction is normally a complex mixture of hydrocarbons whoseboiling points are extremely close together and because the petroleumfraction contains numerous cyclic compounds which tend to' form constantboiling or azeotropic mixtures. As hereinbefore stated, the basis of asolvent extraction separation is the difference in solubility in a givensolvent of one of the substances to be separated from the other. thisdifference the easier the separation will be and an easier separationreflects itself process-wise in less expensive equipment and greateryields per pass in the use of processing equipment as well as in higherpurity A particularly preferred solvent for separating aromatichydrocarbons from non-aromatic hydrocarbons is a mixture of water and ahydrophilic organic solvent. Such a solvent may have its solubilityregulated by adding more or less Water thereto. Thus, by adding morewater to the solvent, the solubility of all components in thehydrocarbon mixture are reduced, but the solubility difference betweenthe components is increased. This effect is reflected process-wise inless contacting stages required to obtain a given purity of product.However, a greater throughput of solvent must be used in order to obtainthe same amount of material dissolved.

As hereinbefore stated, the solvent to be used in this invention ispreferably a mixture of a hydrophilic organic solvent and water, whereinthe amount of water contained in the mixture is selected to regulate thesolu-` bility in the solvent of the materials to be separated. Suitablehydrophilic organic solvents include alcohols,

glycols, aldehydes, glycerine, phenol, etc. Particular preferredsolvents are diethylene glycol, triethylene glycol, dipropylene glycol,tripropylene glycol and mixtures4 thereof containing from about 1% toabout 20% weight of water. sulfur diomde, etc., may be used.

It may, therefore, be seen that the more extreme.

Other hydrophilic substances such as.

In classifying hydrocarbon type compounds according to increasingsolubility in such a solvent, it is found that the solubility of thevarious classes increases in the following manner: the least soluble arethe paraffins followed in increasing order of solubility by naphthenes,olefins, diolefins, acetylenes, sulfur, nitrogen, and oxygen-containingcompounds and aromatic hydrocarbons.

' of the paraiiin with the lower boiling or lighter paraffins being moresoluble than the higher boiling or heavier paraffins. Therefore, whenheavy paraffns are dissolved in the solvent they may be displaced fromthe solvent by adding lighter paraflins thereto. In an embodiment ofthis invention it is preferred to recycle and reform the heavierparafi'ins in the first reaction zone and, therefore, a light parafin ischarged to the extraction zone to displace these heavier parafi'ins fromthe solvent by putting the heavier paraliins into the rainate. The lightparafiins which are introduced to the extraction zone are the isohexanesand lighter parains which are removed as overhead from fractionation ofthe raffinate.

It is an essential feature of the present invention that the rafiinatefrom the extraction zone is passed to a fractional distillation zone inwhich the raffinate is fractionated into at least two fractions, that isa low boiling fraction and a high boiling fraction. We have discoveredand our invention is based on this discovery that when the rafiinate isfractionated into at least two fractions that the optimum operatingconditions for reforming the low octane number higher boiling fractionare those existing in the first reaction zone and, therefore, in apreferred embodiment of the present invention the higher boilingfraction is recycled to the first reaction zone. The low octane numberlower boiling fraction, however, requires different operating conditionsand the lower boiling fraction is reformed in a second reaction zone inwhich the catalyst and conditions are such that a maximum product ofhigh octane gasoline is achieved. In some cases the heavy boilingfraction may contain cornponents which are heavier than is desirable torecycle to the first reforming zone. For example, the raffinate maycontain heavy aromatics, that is, aromatics boiling above about 400 F.and upon recycling heavy aromatics to the first reforming zone, theseheavier aromatics have a tendency to condense and form carbonaceousmaterial on the catalyst and to deactivate the same. In a preferredembodiment of the present invention the heavy fraction of the raffinateis further fractionated to remove heavy components therefrom, that is,components boiling above about 400 F. The heavy raffinate substantiallyfree of components boiling above about 400 F. is then preferablyrecycled to the rst reforming zone. The exact temperature at which theraffinate is split in general depends upon the character of thecomponents in the raffinate; however, we have found that generally thesplit may be made at about 250 F., that is, the end point of the lowboiling fraction is about 250 F. and the initial boiling point of theheavy parafiin fraction is about 250 F. The low boiling rainatetherefore has an initial boiling point of from about n-hexane to about200 F. and a preferred end point within the range of from about 240 F.to about 260 F. The heavy raffinate has a preferred initial boilingpoint within the 240-260 F. range and an end point within the 375-425 F.range.

The light raffinate from the fractionation zone is passed to a secondreforming zone in which a dehydrocyclization catalyst anddehydrocyclization conditions are maintained. As hereinbefore mentioned,the use of a second reaction zone or a dehydrocyclization zone, ispreferred since the conditions in the second zone may be selected so asto produce the highest possible yield of aromatics from the second zonecharge stock, which consists almost essentially of all parainichydrocarbons. The efliuent from the second reaction zone is recycled tothe first fractionation zone or stabilizer and the aromatics present inthe effiuent from the second reaction zone are ultimately removed in theextractor. It is also preferred that the catalyst in the second reactionzone promotes parain isomerization.

Additional features and advantages of our invention will be apparentfrom the following description of the accompanying drawing whichillustrates a particular method for conducting a gasoline reformingoperation in accordance with the present invention.

Referring now to the drawing, there is indicated a l50 F. to 400 F.gasoline charge stream being passed by way of line l and valve 2 intoheater 3 while in admixture with hydrogen being recycled by way of line4. This gasoline stream may be a straight-run gasoline, natural gasolineor other relatively low octane number stream. which is to undergoreforming to provide a high yield of aromatic hydrocarbons, togetherwith desirable high octane number aviation and motor fuels. A heatedstream at a temperature of the order of about 920 F., while at apressure of the order of 600 pounds per square inch is introduced by wayof line 5 into reactor 6.

Reforming reactor 6 contains a bed of spherical catalyst ofapproximately 1A: inch average diameter containing 0.3% platinum, 0.5%combined fluorine, and 0.1% combined chlorine. During the passage of thecharging stock through the first reactor 6 the bulk of thenaphthenescontaining six or more carbon atoms per molecule are dehydrogenated tothe corresponding aromatics and a portion of the parafiins arehydrocracked to lower boiling parafiins. Some isomerization of theparaflins and some dehydrocyclization of the paraflins in the chargepreferably also takes place. The drawing indicates a single conversionzone 6, however, it is to be understood that one or more zones may beutilized in series, with interheaters therebetween if desired, so thatthere may be accomplished a substantial degree 0f aromatization of thecharge stream.

At the conditions in the reforming zone or reactor 6 and in the presenceof hydrogen and the catalyst of this process, olefinic materials willnot be produced in any appreciable amounts.

The resulting reformed stream passes from the first reaction zone 6 byway of line 7, cooler 8 and line 9 and subsequently enters receiver 10.A resulting hydrogencontaining gaseous stream is discharged from theupper portion of receiver 10 by way of line 11 and a portion of thisstream may be vented or withdrawn as fuel gas or process gas by way oflines 12 and 46 and valve 47 while the remaining portion passes by wayof valve 14 into compressor 15. In a preferred operation all of theexcess gas in line 12 passes through lines 12 and 45 to provide ahydrogen atmosphere in reactor 116. In such an operation valve 47 wouldbe in a closed position. The latter provides for compressing andrecycling a portion of the hydrogen-containing stream by way of line 4into heater 3 and again into conversion zone 6. A condensed hydrocarbonstream is passed from receiver 10 by way of line 16 and valve 17 andenters a first fractionation zone or stabilizer 1S. In accordance withthe present invention, normally gaseous hydrocarbons are removedoverhead through line 20. In stabilizer 18 the normally gaseousmaterial, which includes hydrogen, ammonia, hydrogen sulfide, andhydrocarbon gases containing from one to four carbon atoms per molecule,is separated from the hydrocarbon liquid comprising Laromatichydrocarbons and paraiinic hydrocarbons.

germes The gaseous material passes overhead through line 20 into cooler21, wherein a portion of the material is condensed and the entire streampasses through line 22 into receiver 23. In receiver 23 the liquid phaseand the gaseous phase of the overhead material separate; the gaseousmaterial passes through line 25 from which it may be vented to theatmosphere or used as fuel or may be further used in the present processor other processes. The stabilizer has heat provided thereto byreboilerv27 and connecting lines 26 and 28. It is contemplated that thestabilizer and receiver will operate at a sufficient pressure to liquefyat least a portion of the overhead material so that a'liquid refluxstream may be available to improve the separation in stabilizer 18. Theliquid reflux is removed from receiver 23 through line 24 and passesinto an upper portion of stabilizer 18. A portion of the liquid phase inreceiver 23 may be removed through line 23.

The stabilizer bottoms, which as hereinbefore stated, comprisessubstantially parafhnic and aromatichydrocarbons, is withdrawn fromstabilizer 18 through lines 26 and 29 and passed into an intermediatesection of extractor 30. In extractor 3i) the hydrocarbon material risesand is countercurrently contacted at an elevated temperature with adescending stream of selective solvent. In this embodiment diethyleneglycol is used with the latter entering the upper portion of extractor30 through line 32. Water may also be introduced into extractor 30through line 33 containing valve 34 which is shown as being added to theglycol stream in line 32, however, the water may also be added toextractor 30 independently of line 32, that is, it may be separately fedinto extractor 3i). As hereinbefore mentioned, the water is added toincrease the selectivity of the solvent.

As a result of the countercurrent contact of the selective solvent andthe hydrocarbon charge stock introduced via line 29, the aromatichydrocarbons contained in the charge to the extractor are selectivelydissolved in the solvent thereby forming an extract stream 35 containingthe solvent and aromatic hydrocarbons, and a raffinate stream 31containing the paraffinic hydrocarbons. The rafiinate stream passes fromthe upper portion of extractor 30 through line 31 while the extractstream passes through the lower portion of extractor 30 Ithrough line35. Line 35 passes to flash drum 36. Flash drum 36 is maintained at apressure lower than the extractor and preferably is kept at aboutatmospheric pressure. ln the flash drum some of the light parafliniccomponents are flashed overhead and are removed through line 3S.. Theremainder of the liquid is withdrawn from flash drum 36 through line 37and introduced to stripper 41 wherein the dissolved aromatichydrocarbons and dissolved parans are separated from the selectivesolvent. Line 37 is preferably connected to the stripper 41 at a pointin the upper half of the column. The separation in the stripper t1 isnot difcult as the aromatic hydrocarbons are substantially different innature from the selective solvent as well as having a substantiallydifferent boiling point. The aromatic hydrocarbon stream along with somelight paraiins passes overhead from the stripper 41 thro-ugh line tilland combines with the overhead from the flash drum in line 38 and thecombined stream in line 39 is recovered as product or may be furtherblended with other product streams. Heat `is lprovided for the strippingoperation by reboiler 43 and connecting lines 42 and 44. The solventstream is taken from the bottom of stripper l1 through lines 42 and 32and is passed into the upper por-tion of extractor 30 as hereinbeforementioned.

The raffinate stream from extractor 30, which is withdrawn through line31 is fractionated into at least two fractions. The raffinate alsocontains dissolved and entrained solvent and the raffinate may be Waterwashed to remove the solvent before recycling any fractions of theraffinate to the reforming zone. In the drawing the raffinate in line 31is introduced into fractionator 50.

Fractionator 5() is preferably .operated as a deisohexanizer". Theconditions in deisohexanizer 50 are maintained so that the componentslighter than those which it is preferred to reform are removed as anoverhead fraction. In the embodiment of the drawing, the overhead isshown as comprising components boiling below normal hexane, that is, theoverhead fraction contains isohexane and lighter components. Thesecomponents are removed from fractionator 50 through line 51 and passinto cooler 52 wherein the material is condensed and the entire streampasses through line 53 into receiver 54. The liquid in receiver S4splits up into several streams. A portion of the liquid in receiver 54is withdrawn through line 55 and introduced into the upper portion ofdeisohexanizer 50 as reflux. A portion of the liquid in receiver 54 maybe withdrawn through line 56 as product and in some instances may becombined with the product in line 39. As illustrated inthe drawing onlya portion of the liquid product in receiver 54 is withdrawn as productthrough lines 56 and 56 while the remainder of fthe light fraction iswithdrawn through line 56 and passed to a lower portion of extractor3l). This use of the isohexane and lighter fraction in line 56, that isas redux to extractor 30, is a preferred feature of the invention. Theuse of this isohexane and lighter fraction enables more of the heavierparatiins to be recycled to the reforming reactor and this combinedoperation provides a greater utilizing of the product streams andultimately increases the yield and octane number of the nal product.Heat is provided for the fractionating in fractionator S0 by reboiler 58and connecting lines 57 and 59. The bottoms, which are substantiallyfree of components boiling below normal hexane, are removed fromdeisohexanizer 50 through lines 57 and 60. A portion of the liquid in.line 60 may be withdrawn as product through line 61, however, it ispreferred that all the liquid in line 61 passes through line 62 intofractionator 70. Fractionators 70 and 90 operate so as to provide a lowboiling predominantly parafiinic fraction and a high boilingpredominantly parainic fraction, with the low boiling fraction reformedin second reaction zone 116 While the heavier fraction is recycled toreforming reactor 6, all of which is hereinafter described in detail.

The normal hexane and heavier fraction in line 62 is introduced intofractionator 7i). Fractionator 70 has heat provided thereto by reboilerand connecting lines '79 and 81. A light fraction is removed overheadthrough line 71 and the fraction passes through cooler 72 and line 73into overhead receiver 74. Some of the liquid is withdrawn from receiver74 through line 75 and introduced into an upper pontion of fractionator79 as reliux. In the embodiment herein illustrated the fractionator isoperated so that the end point of the liquid in receiver 74 is about 250F. The liquid fraction in receiver 74 therefore contains componentsboiling from normal hexane 'to about 250 F. A portion of the normalhexane-250 F. fraction is withdrawn from receiver 74 through line 76. Aportion of the liquid in line 76 may be withdrawn as product throughline 77, however,- it is preferred that all the liquid be withdrawnthrough'lines 76 and 78 and subjected to reforming in reactor 116. Thenormal hexane-250 F. fraction in line 78 is picked up by pump 111 anddischarged into line 112 and combines with a hydrogen-rich gas Stream45, prepared as hereinbefore specied, and the mixture of light raffinateand hydrogen in line 113 passes into heater 114- wherein the combinedstream is heated to a. temperature of the order of about 920 F. Thepres,- sure in the second reaction zone is in the order of 400 poundsper square inch. As hereinbefore mentioned, the pressure in `the secondreaction zone 116 is at least 75 pounds per square inch lower than thepressure in the first reaction zone 6 and preferably is at least 100Apounds per square inch lower.

Thecombined stream is heated in heater 114 and.

. i 11 passes through line 115 into reactor 116. Reforming reactor 116contains a bed of spherical catalyst of the same composition of thecatalyst in reactor 6. During the passage of the charge stock throughthe second reactor 116 a substantial portion of the paraflins containingsix or more hydrocarbons per molecule are dehydrocyclicized to thecorresponding aromatics and a portion of the parains are hydrocracked tolower boiling paralins. A substantial portion `of the paraffins are alsoisomerized, for example, normal hexane is isomerized to isohexane. Thedrawing indicates a single conversion zone 116, however, it is herebyunderstood that one or more zones may be utilized in series withinterheaters between as desired so that there may be accomplished asubstantial degree of dehydrocyclization of 'the charge stream. Theconditions in the reforming zone of reactor 116 are selected so thatthere is substantial dehydrocyclization and isomerization of parafns andso that there are substantially no olenic substances produced. At theconditions hereinbefore specified, and in the presence of hydrogen andthe catalyst of this invention, olefinic materials will not be producedin any appreciable amounts.

The effluent stream from reactor 116 passes by Way of line 117, cooler118, line 120 and subsequently enters a separating zone or receiver 121.A resulting hydrogencontaining gaseous stream is discharged from theupper portion of receiver 121 by way of line 125 and a portio-n of thisstream may be vented or withdrawn as fuel gas or process gas by way ofline 125 and a portion may be recycled by means of a compressor to thereaction zone 116. Suicient hydrogen may be introduced through line 45so that recycling of the hydrogen in line 125 may be unnecessary. Thecondensed hydrocarbon stream is withdrawn from separator 121 by way ofline 126. The liquid in line 126 is introduced to stabilizer 18 throughline 16.

A heavy predominantly parafnic fraction is withdrawn from fractionator70 through lines 79 and 82. A portion of the liquid inline 82 may bewithdrawn as product through 83, however, it is preferred that all ofthe liquid in line 82 pass through line 84 into fractionator 90.Fractionator 90 is operated so that components that are heavier than aredesirable to recycle to reforming reactor 6 are removed as bottoms. Wehave discovered that the fraction boiling above about 400 F. ispredominantly aromatic and, therefore, no benefits can be obtained inrecycling the 400 F.-| fraction to the reactor 6. In fact, recycling the400 F.| fraction to the first reactor 6 may cause excessive deactivationof the catalyst by coking of the same. In a preferred embodiment of thepresent invention the extractor 30 is operated at rather moderateconditions so that a considerable amount of the heavy aromatics arepresent in the raffinate and these heavy aromatics are subsequentlyremoved as bottoms in fractionator 90. The economics of the operationare definitely in favor of operating extractor 30 at moderate conditionsand removing the aromatics in fractio-nator 90 instead of in the extractin line 35. Fractionator 90 has heat provided hereto by reboiler 99 andconnecting lines 98 and 100. The 400 F. and heavier fraction may beremoved from fractionator 90 through lines 98 and 110. The heavy productin line 110 may be combined with other product streams.

The overhead material from fractionator 90 is withdrawn through line 91,passes into cooler 92, line 93 and enters receiver 93. A portion of theliquid in receiver 93 is withdrawn as reflux through line 94 andintroduced into an upper portion of' fractionator 90 to aid in theseparation of the hydrocarbons. The material in line 93, in theembodiment herein illustrated, comprises hydrocarbons boiling betweenabout 250 F. and 400 F. A portion of the 250 F. to 400 F. fraction inreceiver 93 is Withdrawn through line 95. A portion of the heavyfraction in line 95 may be withdrawn through line 96 as product,however, a portion of the liquid in line passes through line 97 and isrecycled to line 1 to eventually pass into the first reforming zone 6.

Although the process illustrated in the ydrawing represents one of thepreferred forms of our invention, it is to be understood that ourinvention is not limited thereby. A number of variations may beintroduced into the process without departing from the spirit and scopeof said invention.

The following example is given to further illustrate our invention, butit is not given for the purpose of unduly limiting the generally broadscope of said invention.

Example A naphtha fraction having an initial boiling point of 189 F. andan end boiling point of 395 F. is passed through a bed ofplatinum-alumina-combined halogen catalyst comprising alumina containing0.3% by weight of platinum and 0.2% by weight of uorine, at a pres.-sure of 700 pounds per square inch, a hydrogen to hydrocarbon mol ratioof 6, a weight hourly space velocity of 4, and an initial averagecatalyst temperature of 900 F.

The eluent from the reaction zone is cooled and the C4 and lightercomponents removed by fractional distillation. The remaining liquid iscountercurrently contacted in a sieve deck tower with a descendingstream of 97% diethylene glycol and 3% Water. The contact is effected at300 F. and approximately 175 pounds per square inch pressure. Theraflinate is removed from the top of the tower and the extract isremoved from the bottom of the tower. The aromatics are recovered fromthe extract by fractional distillation. The raiiinate is fractionated toform a low boiling fraction having an initial boiling point of F. and anend boiling point of 248 F. and a high boiling fraction having aninitial boiling point of 248 F. and an end point of 400 F.

The low boiling fraction is passed through a bed ofplatinum-alumina-combined halogen catalyst comprising alumina containing0.3% by weight of platinum and 0.2% by Weight of uorine at a pressure of400 pounds per square inch, a hydrogen to hydrocarbon mol ratio of 5, aweight hourly space velocity of 3, and an initial average catalysttemperature of 910 F. The eluent from this second reaction zone iscombined with the aromatics recovered from the extract. The blend is anexcellent motor fuel of high octane number and good startingcharacteristics.

We claim as our invention:

1. A hydrocarbon conversion process which comprises catalyticallyreforming a gasoline fraction in a first reforming zone, subjectingsubstantially all of the resultant reformed gasoline products to solventextraction to separate the same into a paranic raflinate and an aromaticconcentrate, recovering said aromatic concentrate as a product of theprocess, fractionating said rainate to separate therefrom a relativelylight fraction having an end boiling point in the range of about 24U-260F. and a heavier fraction boiling in the range between said end pointand about 400 F., reforming said light fraction in a second reformingzone at a pressure at least 75 pounds per Square inch lower than thepressure in said first reforming zone, and recycling said heavierfraction to said first reforming zone.

2. A hydrocarbon conversion process which comprises catalyticallyreforming a gasoline fraction in the presence of hydrogen in a firstreforming zone, separating a hydrogen-containing gas from the resultantreformed gasoline products, subjecting substantially all of saidgasoline products to solvent extraction to separate the same into aparainic ranate and an aromatic concentrate, recovering said aromaticconcentrate as a product of the process, fractionating said rainate toseparate there-v from a relatively light fraction having an end boilingpoint in the range of about 240-260 F. and a heavier fraction boiling inthe range between said end point and about 400 F., reforming said lightfraction in a second reforming zone in the presence of at least aportion of said hydrogen-containing gas and at a pressure at least 75pounds per square inch lower than the pressure in said first reformingzone, and recycling said heavier fraction to said first reforming zone.

3. A hydrocarbon conversion process which comprises catalyticallyreforming a gasoline fraction in a first reforming zone, stabilizing theresultant hydrocarbon products in a stabilizing zone to separatenormally gaseous hydrocarbons from the reformed gasoline, subjectingsubstantially all of the stabilized reformed gasoline to solventextraction to separate the same into a parainic rainate and an aromaticconcentrate, recovering said aromatic concentrate as a product of theprocess, fractionating said rainate to separate therefrom a relativelylight fraction having an end boiling point in the range of about 240`260o F. and a heavier fraction boiling in the range between said endpoint and about 400 F., reforming said light fraction in a secondreforming zone at a pressure at least 75 pounds per square inch lowerthan the pressure in said first reforming zone, recycling said heavierfraction to said first reforming zone, and supplying the reformedproducts from said second reforming zone to said stabilizing zone forstabilization thereintogether with said hydrocarbon products from therst reforming zone.

4. A hydrocarbon conversion process which comprises catalyticallyreforming a gasoline fraction in the presence of hydrogen in a rstreforming zone, separating a hydrogen-containing gas from the resultanthydrocarbon products, stabilizing the latter in a stabilizing zone toseparate normally gaseous hydrocarbons from the reformed gasoline,subjecting substantially all of the stabilized reformed gasoline tosolvent extraction to separate the same into a paraflinic rainate and anaromatic concentrate, recovering said aromatic concentrate as a productof the process, fractionating said raffinate to separate therefrom arelatively light fraction having an end boiling point in the range ofabout 240-260 F.

and a heavier fraction boiling in the range between said end point andabout 400 F., reforming said light fraction in a second reforming zonein the presence of at least a portion of said hydrogen-containing gasand at a pressure at lea'st 75 pounds per square inch lower than thepressure in said first reforming zone, recycling said heavier fractionto said rst reforming zone, and supplying the reformed products fromsaid second reforming zone to said stabilizing zone for stabilizationtherein together with said hydrocarbon products from the first reformingzone.

5. A hydrocarbon conversion process which comprises catalyticallyreforming a gasoline fraction in a first reforming zone, subjectingsubstantially all of the resultant reformed gasoline products to solventextraction to separate the same into a parainic raffinate and anaromatic concentrate, recovering said aromatic concentrate as a productof the process, fractionating said raliinate to separate therefrom arelatively light gasoline fraction and a heavier gasoline fraction., andreforming said light fraction in a second reforming zone underindependently controlled reforming conditions.

6. The process of claim 5 further characterized in that said heaviergasoline fraction is recycled to the first reforming zone.

References Cited in the file of this patent UNITED STATES PATENTS2,400,802 Arnold May 21, 1946 2,409,695 Laughlin Oct. 22, 1946 2,479,110Haensel Aug. 16, 1949 2,697,684 Hemminger et al Dec. 21, 1954 2,710,826Weikart .lune 14, 1955 2,767,124 Myers Oct. 16, 1956 OTHER REFERENCESRelation of Properties to Molecular Structure for PetroleumHydrocarbons, by Cecil E. Boord, Progress in Petroleum Technology, pages364 and 365, American Chem. Society, Washington, D.C., published Aug. 7,1951.

1. A HYDROCAARBON CONVERSION PROCESS WHICH COMPRISES CATALYTICALLYREFORMING A GASOLINE FRACTION IN A FIRST REFORMING ZONE, SUBJECTINGSUBSTANTIALLY ALL OF THE RESULTANT REFORMED GASOLINE PRODUCTS TO SOLVENTEXTRACTION TO SEPARATE THE SAME INTO A PARAFFINIC RAFFINATE AND ANAROMATIC CONCENTRATE, RECOVERING SAID AROMATIC CONCENTRATE AS A PRODUCTOF THE PROCESS, FRACTIONING SAID RAFFINATE TO SEPARATE THEREFROM ARLATIVELY LIGHT FRACTION HAVING AN END BOILING POINT IN THE RANGE OFABOUT 240-260*F. AND A HEAVIER FRACTION BOILING IN THE RANGE BETWEENSAID END POINT AND ABOUT 400*F., REFORMING SAID LIGHT FRACTION IN ASECOND RFORMING ZONE AT A PRESSURE AT LEAST 75 POUNDS PER SQUARE INCHLOWER THAN THE PRESSURE IN SAID FIRST REFORMING ZONE, AND RECYCLING SAIDHEAVIER FRACTION TO SAID FIRST REFORMING ZONE.